Apparatus for measuring total pressure and partial pressure with common electron beam

Abstract

An apparatus for determining both total and partial pressures of a gas using one common electron beam includes a partial pressure ionization region and a total pressure ionization region separated by a grid or aperture. A filament produces a plurality of electrons which are focused into an electron beam by a repeller and an aperture or an anode. The interaction between the electron beam and molecules of the gas within the partial pressure and total pressure regions produces first and second ion streams. A focus plate is biased such that the first ion stream is directed to an analyzer which calculates the partial pressure of the gas. An ion collector collects the ions from the second ion stream, where the resulting reference current is used to determine the total pressure of the gas.

What is claimed is:  
     
       1. An apparatus for determining a total pressure of a gas, comprising: 
       an ionization chamber;  
       said ionization chamber having adjacent first and second ionization regions, wherein a boundary between said adjacent ionization regions is defined by one of an aperture and an anode grid;  
       means for producing an electron beam passing through each of said first and second ionization regions, whereby an interaction between said electron beam and molecules of said gas within said ionization chamber produces first and second ion streams from a same gas density;  
       means for directing said first ion stream from said first region to an analyzer; and  
       means for directing said second ion stream from said second region to an ion collector.  
     
     
       2. An apparatus according to  claim 1 , further comprising: 
       means for collecting said second ion stream at said ion collector;  
       means for measuring a reference current produced by said second ion stream at said ion collector; and  
       means, using said reference current, for calculating said total pressure of said gas within said ionization chamber.  
     
     
       3. An apparatus according to  claim 2 , wherein said analyzer includes means for calculating at least one partial pressure of said gas within said ionization chamber. 
     
     
       4. An apparatus according to  claim 3 , further comprising an electron beam stop which collects substantially all electrons not interacting with said gas molecules. 
     
     
       5. An apparatus according to  claim 4 , wherein said means for producing an electron beam comprises: 
       emission means for emitting a plurality of electrons; and  
       focusing means for focusing said plurality of electrons into said electron beam.  
     
     
       6. An apparatus according to  claim 1 , wherein said means for producing an electron beam comprises: 
       emission means for emitting a plurality of electrons; and  
       focusing means for focusing said plurality of electrons into said electron beam.  
     
     
       7. An apparatus according to  claim 6 , wherein said focusing means includes a repeller having three sides and an opening for said electron beam to pass through. 
     
     
       8. An apparatus according to  claim 1 , wherein said anode grid has a rectangular cross-section. 
     
     
       9. An apparatus according to  claim 8 , wherein said anode grid includes a flat portion that is oriented perpendicular to said electron beam. 
     
     
       10. An apparatus according to  claim 1 , wherein said electron beam passes through said first ionization region before said electron beam passes through said second ionization region. 
     
     
       11. An apparatus according to  claim 1 , wherein said electron beam passes through said second ionization region before said electron beam passes through said first ionization region. 
     
     
       12. An apparatus according to  claim 1 , wherein said collector is arranged parallel to said analyzer. 
     
     
       13. An apparatus for determining a total pressure of a gas, comprising: 
       an ionization chamber;  
       said ionization chamber having adjacent first and second ionization regions, wherein a boundary between said regions is defined by one of an aperture and an anode grid;  
       a filament for producing a plurality of electrons;  
       a repeller;  
       said repeller and anode operatively associated to focus said plurality of electrons into an electron beam passing through each of said first and second ionization regions, whereby an interaction between said electron beam and molecules of said gas within said ionization chamber produces first and second ion streams from a same gas density;  
       a focus plate biased such that said first ion stream is directed from said first ionization region to an analyzer, wherein said analyzer includes means for calculating at least one partial pressure of said gas within said ionization chamber;  
       an ion collector biased such that said second ion stream is directed from said second ionization region to an ion collector;  
       means for measuring a reference current produced by said second ion stream at said ion collector; and  
       means, using said reference current, for calculating said total pressure of said gas within said ionization chamber.  
     
     
       14. An apparatus according to  claim 13 , wherein said anode grid has a rectangular cross-section. 
     
     
       15. An apparatus according to  claim 14 , wherein said anode grid includes a flat portion that is oriented perpendicular to said electron beam. 
     
     
       16. An apparatus according to  claim 13 , wherein said collector is arranged in parallel to said analyzer. 
     
     
       17. A method for determining a total pressure of a gas, comprising the steps of: 
       providing an ionization chamber, said ionization chamber having adjacent first and second ionization regions, wherein a boundary between said adjacent ionization regions is defined by one of an aperture and an anode grid;  
       producing an electron beam passing through each of said adjacent first and second ionization regions, whereby an interaction between said electron beam and molecules of said gas within said ionization chamber produces first and second ion streams from a same gas density;  
       directing said first ion stream from said first ionization region to an analyzer; and  
       directing said second ion stream from said second adjacent ionization region to an ion collector.  
     
     
       18. A method according to  claim 17 , further comprising the steps of: 
       collecting said second ion stream at said ion collector;  
       measuring a reference current produced by said second ion stream at said ion collector; and  
       calculating, using said reference current, said total pressure of said gas within said ionization chamber.  
     
     
       19. An apparatus according to  claim 17 , including the step of arranging said analyzer in parallel alignment with said collector.